1. Field
The present disclosure relates to control methods and systems applied to prosthetic devices and to methods and systems that incorporate and/or investigate neural bases of behavior.
2. Related Art
All publications herein are incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Eye movements may be broadly categorized into those that are voluntary and those that are involuntary. Among other things, involuntary eye movements compensate for head movement; account for a moving background behind an object on which vision is focused; and act in a reflexive manner to external stimuli. At least certain voluntary eye movements, on the other hand, are known to relate to motor coordination and other behavioral attributes and processes.
Most voluntary eye movements are properly classified as saccades, as smooth pursuit eye movement, or as vergence movement. Saccades and smooth pursuit eye movement relate to two dimensions in a visual field (i.e., the x- and y-axis in a coordinate system), while vergence movement accounts for depth (i.e., the z-axis). More particularly, saccades are eye movements in which the eyes rapidly jump from one point to another (e.g., from one word to the next while reading or around a room when searching for an object); smooth pursuit eye movement involves eye movements that smoothly track slowly moving objects in the visual field; and vergence movement—a relatively slow eye movement—occurs when both eyes coordinate to form an angle in a particular gaze direction (e.g., to focus on an object at a particular depth in the visual field). Voluntary eye movements act in concert with other physiological functions, such as motor function and psychological features of perception, to coordinate behavior. Based on the coordinated nature of behavior, measurements of voluntary eye movement as a function of time enable the prediction of movement.
Eyes move so quickly and easily that voluntary eye movements, generally, and saccadic eye movements, in particular, are a central feature of primates' natural behavior. Voluntary eye movements are not only crucial for visual perception, but they also play an important role in motor control and provide visual guidance for action. Indeed, orchestration of hand and eye movements as we look and reach occurs frequently in natural behavior (D. H. Ballard et al., Spatio-temporal organization of behavior, Spatial Vision, 13:321-333 (2000); Land, M. F. & Hayhoe, M., In what ways do eye movements contribute to everyday activities?, Vision Res., 41:3559-3565 (2001)). In addition to these sensory and motor roles, voluntary eye movements also participate in higher cognitive processes. They are involved in shifting the locus of spatial attention and both reflect and influence preferences and decisions (H. Scherberger et al., Target selection for reaching and saccades share a similar behavioral reference frame in the macaque, J. Neurophysiol., 89:1456-1466 (2003)). Studies of eye movements in humans under naturalistic conditions reveal saccades are part of strategies to limit the cognitive demands of a task (Land, M. F. & Hayhoe, M., In what ways do eye movements contribute to everyday activities?, Vision Res., 41:3559-3565 (2001); M. M. Hayhoe et al., Visual memory and motor planning in a natural task, J. Vis., 3:49-63 (2003); H. Scherberger et al., Target selection for reaching and saccades share a similar behavioral reference frame in the macaque, J. Neurophysiol., 89:1456-1466 (2003)). Despite this multiplicity of roles in higher brain function, however, there has been relatively little physiological work studying eye movements when the eyes are free to move. In fact, most studies of eye movements have employed tasks with explicit instructions that require controlled fixation. While allowing a degree of experimental tractability, this approach is not well-suited for understanding voluntary eye movements, such as saccades, and the underlying brain mechanisms during natural behaviors.
Another hallmark of natural behavior is decision-making. A body of work now implicates a number of cortical areas in the neural basis of decision-makings; in particular, sensory-motor areas in the parietal cortex having strong anatomical connections with each other and with areas in the frontal cortex. Neuronal activity in these distributed networks can be divided into two distinct classes: spiking and local field potential (LFP) activity. Spiking is due to action potentials from individual cells while field potentials reflect synaptic activity and return currents from a population of cells near the tip of the recording electrode (U. Mitzdorf, Current source-density method and application in cat cerebral cortex: investigation of evoked potentials and EEG phenomena, Physiol. Rev., 65:37-100 (1985)). Recent work studying area LIP and PRR in the posterior parietal cortex shows that LFP activity as well as spiking reflects information processing (Scherberger, H., Jarvis, M. R., and Andersen, R. A., Cortical Local Field Potential Encodes Movement Intentions in the Posterior Parietal Cortex, Neuron, 46:347-354 (2005)). Despite the results showing that natural behavior critically depends on higher cortical function, there has been little direct work on this at a physiological level.
Recent work in multiple institutions has demonstrated the feasibility of a neural prosthetic based on cortical recordings. Some of this work focused on decoding motor variables, such as movement trajectory (M. D. Serruya et al., Instant neural control of a movement signal, Nature, 416:141-142 (2002); J. M. Carmena et al., Learning to control a brain-machine interface for reaching and grasping by primates, Plos Biol., 1:193-208 (2003); D. M. Taylor et al., Direct cortical control of 3D neuroprosthetic devices, Science, 296:1829-1832 (2002)), while other work decodes cognitive variables such as movement goals and expected value (S. Musallam et al., Cognitive control signals for neural prosthetics, Science, 305:258-262 (2004)). But, whether coordinated eye movements could also be used for this application was heretofore an open question.
There is therefore a need in the art for systems and methods that incorporate measurements of eye movement—and particularly, voluntary eye movement—in the mechanisms that control neural prosthetics, either alone or in combination with cortical recordings relating to other functions, such as decision-making.